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Both the Pfizer and AstraZeneca COVID-19 vaccines showed effectiveness against symptomatic disease from B.1.617.2, the so-called Indian variant, British researchers found.

Two doses of Pfizer's vaccine showed 87.9% efficacy (95% CI 78.2%-93.2%) against the variant, while two doses of AstraZeneca's showed 59.8% efficacy (95% CI 28.9%-77.3%), reported Jamie Lopez Bernal, PhD, of Public Health England in London, and colleagues in a online.

Vaccine effectiveness after one dose against B.1.617.2 was similarly low for both vaccines, at 33%.

"This is the first study that we are aware of to report on vaccine effectiveness against the B.1.617.2 variant," the authors wrote.

They used a test negative case-control study, with data on both vaccination status through May 16, 2021 and PCR testing from Oct. 26, 2020 to May 16, 2021. They then used whole genome sequencing or a proxy assay (testing positive or negative on the spike gene target) to identify both the B.1.617.2 variant and the B.1.1.7 variant (the so-called U.K. variant).

Effects of the vaccine were defined as symptom onset 21 days after the first dose until the second dose was administered (one dose), and 14 days after the second dose (two doses).

Overall, 12,675 cases were sequenced, 11,621 of which were B.1.1.7 and 1,054 were B.1.617.2. Cases with B.1.617.2 had a higher proportion of women, a higher proportion of "Indian or Indian British" or "other Asian background" ethnicity, as well as a higher proportion of foreign travel and more recent cases.

Combined vaccine effectiveness was 51.5% for the B.1.1.7 variant. However, after two doses of Pfizer vaccine, effectiveness against B.1.1.7 was 93.4% (95% CI 90.4%-95.5%) compared with 66.1% (95% CI 54.0%-75.0%) with two doses of AstraZeneca's vaccine.

Drop in vaccine effectiveness appeared greater with AstraZeneca's vaccine (OR 1.48, 95% CI 1.18-1.87) compared with Pfizer's (OR 1.17, 95% CI 0.82-1.67).

"These findings suggest a modest reduction in vaccine effectiveness," the authors wrote. "Nevertheless, a clear effect of both vaccines was noted with high levels of effectiveness after two doses."

Limitations to the data include that this was an observational study, so unmeasured confounders are possible, such as differences in populations that received each vaccine. They also noted low sensitivity or specificity of PCR testing could have misclassified individuals as being positive or negative.

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